Ibn Abideen mentions that a prayer performed with a makrooh tahriman act is wajib (necessary) to repeat and only recommended (to repeat) if the makrooh is tanzihan (minor dislike).

Common mistake #1

It is makruh tahriman (close to haram) to fold your trousers specifically for Salah. You should perform the prayer without folding them.

If the trousers are below the ankles and you have no pride then this would be makruh tanzihan (minor dislike). And you would not need to repeat the prayer. If you have pride wearing long garments this is haram and the prayer would need to be repeated.

If you trousers are folded all the time outside of prayer too, then it will not be makruh tahriman to pray in them in that state.

As for the Prophet's saying: "the one who makes his garment hang down on the ground" then its meaning is: The one who lets it down and drags its extremity OUT OF ARROGANCE (KHAYLA')... Imam Nawawwi

Sisters should note that praying in see-through clothes/scarves will also make your prayer invalid. The awrah for them is the full body except face, hands & feet.

Common mistake #4

It is obligatory to start the prayer saying 'Allahu Akbar', this must be recited for the prayer to start. This is for both praying alone or praying in a congregation.

Any prayers without the takbir e tahrima (opening takbeer) are invalid.

Common mistake #5

It is obligatory to recite the Qur'an in the prayer when praying alone. It is not sufficient to be thinking of the verses in your mind, they must be uttered and you should be able to hear yourself. Not doing this will invalidate the prayer because qiraat is a compulsory pillar of the prayer.

It is wajib (necessary) to remain silent (for surah fatiha & the other surah) when praying behind an Imam, his recitation suffices for all those behind him (thana, tasbih, tashahud & durood is recited as normal). To recite the Qur'an when praying behind an Imam is makruh tahriman.

Common mistake #6

Self-explanatory. See page 146 of Laws of Salah.

Common mistake #7

Scratching thrice in one rukn (of salah) will invalidate salah i.e. scratching once and then lifting hand, then scratching and lifting hand once again; it is twice-scratching. If the act of scratching is repeated for the third time, salah will become invalid. Placing the hand once (at an organ) and moving it several times will be considered scratching once only.

Common mistake #8

If an adult laughed in a Salah, consisting of Ruku' and Sujud, so loudly that people in vicinity heard his laughing, his Wudu and Salah, both became invalid. If he laughed loudly such that only he listened to it, his Salah will become null (invalid) but there will be no effect on his Wudu. Smiling (without creating a sound) will not nullify Wudu and Salah. (Maraqil Falah, pp. 91)

Folding cloth, as these days, some people lift their trousers etc. from front or rear side while going down for Sajdah is makruh tahriman. However, if the cloth sticks to the body, there is no harm in un-sticking it with one hand. [Laws of Salah]

Common mistake #11 [MEN ONLY]

PLEASE NOTE: the prostration of a woman is different to that of a man. Women do not bend their toes - instead they tilt both feet towards the right. When performing sajdah women must keep the parts of their body close together i.e. arms touching sides, belly touching thighs, thighs touching shins and shins touching the ground with the feet out towards the right.

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"In Sharh Niqāyah of Qahastānī it is stated: The correct opinion is that raising both feet off the ground [in sajdah] nullifies the prayer as is mentioned in al-Qunyah" (al-Fatāwā al-Ridwiyyah vol 7 pg 366)

To bend all five on each foot is Sunnah. [Bahar e Shariat p513 & p530]

Imam Ahmed Rida Khan states, "To rely on the sole of one toe from the 10 toes of the feet in the state of sajdah is fard according to the relied upon and mufta bihī opinion of the Madhab... And to place all or most of the toes of both feet is not far from being wājib."